There is no such setting in the avastUI and as far as I’m aware no .ini file setting that can be manually set.

What is the problem with it popping up ?
If it is because you are working and don’t want the notification (?), you could try pushing it back to a time that the computer is on, but you aren’t likely to be active.

Previously there was no indication that a scheduled scan was running and many were asking for notification it was running, so they a) didn’t shutdown whilst it was running or b) start something that was resource intensive.

You could also set avast into Silent/Gaming mode (avastUI, Settings), that of course would effect all popups, etc. and not just this one.

Another one, I have my avastUI open almost all the time (referring to it when helping in the forums), but minimised to the windows task-bar. I believe when the avastUI is open (even minimised) you don’t get this scheduled scan in progress pop-up.